Melt extruded nonwoven webs have many uses, including medical care garments and products, protective wear garments, mortuary and veterinary products, and personal care products. For these applications, nonwoven fibrous webs provide tactile, comfort and aesthetic properties that approach those of traditional woven or knitted cloth materials. Nonwoven web materials are also widely utilized as filtration media for both liquid and gas or air filtration applications since they can be formed into a filter mesh of fine fibers having a low average pore size suitable for trapping particulate matter while still having a low pressure drop across the mesh.
Melt extrusion processes for spinning continuous filament yarns, filaments or fibers such as spunbond fibers, and for spinning microfibers such as meltblown fibers, are well known in the art, as are the associated processes for forming nonwoven webs or fabrics therefrom. Typically, fibrous nonwoven webs such as spunbond nonwoven webs are formed with a fiber extrusion apparatus, such as a spinneret, and fiber attenuating apparatus, such as a fiber drawing unit (FDU), oriented in the cross-machine direction (“CD”). That is, the apparatus is oriented at a 90-degree angle to the direction of web production (the “machine direction” or “MD”). Although the fibers are laid on the forming surface in a generally random manner, still, because the fibers exit the CD oriented spinneret and FDU and are deposited on the MD-moving forming surface, the resulting nonwoven webs have an overall average fiber directionality wherein more of the fibers are oriented in the MD than in the CD. A fiber diffuser may be positioned below the FDU to reduce the fiber velocity prior to laying the fibers onto the forming surface. It is widely recognized that such properties as material tensile strength, porosity, permeability, extensibility and material barrier, for example, are a function of the material uniformity and the directionality of the fibers or filaments in the web.
Various attempts have been made to distribute the fibers or filaments within the web in a controlled manner, attempts including the use of electrostatics to impart a charge to the fibers or filaments, the use of spreader devices to direct the fibers or filaments in a desired orientation, the use of mechanical deflection means for the same purpose, and reorienting the fiber forming means. For example, WO 2005/045116 describes a method an apparatus for the production of nonwoven web materials wherein the fibers are attenuated with a fiber drawing unit and the velocity of the fibers is reduced in a downstream diffusion chamber defined between opposed diverging sidewalls. An electrostatic charge is applied to the fibers either before they enter the diffusion chamber or within the diffusion chamber by two or more oppositely directed electrostatic charging units.
WO 02/052071 describes a method and apparatus for the production of nonwoven web materials wherein the fibers are subjected to an electrostatic charge and then directed to a deflector device while under the influence of the charge. The fibers are then collected on a forming surface to form the nonwoven web. The deflector device may include a series of teeth separated by a distance determined by the desired orientation of the fibers in the nonwoven web.
The art is continuously seeking improved methods and devices to still further improve the process of distributing the fibers in melt extrusion processes to achieve superior nonwoven materials. The present invention relates to such an improved method and apparatus.